It is important to know the weight of a vehicle during its operation to optimize control of it as the weight and conditions change. Vehicle weight may be a consideration, for example, during loading and unloading, compliance with vehicle load distribution regulations, as well as affecting the fuel efficiency of the vehicle.
Some examples of known methods to determine the weight of a vehicle are described below:
U.S. Pat. No. 5,877,455 teaches a system for determining the weight of a vehicle using accelerometers. A first accelerometer is supported on the front steering axle of the vehicle. The first accelerometer measures the vertical acceleration of the front steering axle. Each additional axle of the vehicle also supports an accelerometer to measure the vertical acceleration of each respective axle. All of the accelerometers are electrically linked to a central processor or electronic control unit. The first accelerometer produces a first signal when the vehicle is moving. The first signal is sent to the ECU. The other accelerometers also send signals that are combined to form a second signal. The first signal and the second signal are compared to determine the weight of the vehicle.
U.S. Pat. No. 5,973,273 provides for a method of determining the weight of a vehicle. The method comprises a single acceleration sensor used to measure vertical acceleration, however, additional acceleration sensors may also be used. In one embodiment, a single linear acceleration sensor is used to measure vertical acceleration of the vehicle and two angular sensors are used to provide pitch and roll data from the vehicle. The patent indicates that all three sensors can be combined into a single sensor unit located together on the vehicle. The sensors can be any type, including mechanical inertial or piezoelectric sensors. The linear sensor can be used to measure acceleration from which an oscillatory frequency can be derived, including vertical velocity. An estimated weight supported by the suspension system is calculated based upon the measured frequency taken together with the predetermined spring properties of the suspension. The sensor, or sensors, may be sensitive to particular frequencies, or filters may be used to remove frequencies caused by the engine or frequencies from other mechanical noise. The estimated weight can be made available via a display to the driver, recorded electronically or otherwise in a vehicle log, and/or serve as an input to other vehicle safety or control systems.
U.S. Pat. No. 6,646,210 teaches a sensor or sensors located on the sprung part of the vehicle, for example, on the vehicle chassis. The sensors are connected to a data storage unit that is located on the vehicle or it may be separate from the vehicle. The sensors register vertical acceleration of the spring vehicle component to which they are attached.
Notwithstanding these efforts, the known methods of vehicle weight determination are still cumbersome and expensive. More specifically, among the disadvantages of known methods are:
The requirement for several accelerometers and also the fact that the accelerometers have to be located at more than one location on the vehicle. Therefore, they cannot be contained within the ECU where the information is ultimately processed. This dictates a requirement for expensive wiring and connectors. This is especially the case since in many known systems, the accelerometers are located on the axles. Continuous suspension motion means that the wiring must be robust and suitable for continuous flexing. Further, in some methods disclosed in the art, acceleration behavior of the axles is strongly influenced by the air pressure in the tires. Even if this is very carefully checked, for example each morning, it changes due to temperature changes while the vehicle is in motion, thus introducing one or more factors which can cause error in weight determination.
Thus, it would be desirable to have an inexpensive system for continuously estimating the weight of an unpowered vehicle, particularly a semi-trailer vehicle which is easily installed and maintained.